The invention refers to a backrest assembly for a wheelchair with a reclining seat.
A wheelchair having a primary articulated member, at least one secondary articulated member, a primary sensor for detecting the position of the primary member, a secondary sensor for detecting the position of the secondary member, and a controller capable of articulating the secondary articulated member as a function of the movement of the primary articulated member, is known from US 2004/094936.
US 2005/0088024 discloses a reclining seat which includes a base, a back frame and back support connected to the back frame for translation relative to the back frame. In a first embodiment, a mechanism is described to couple the back frame to the back support such that rotation of the back frame relative to the base automatically translates the back support relative to the back frame. In a second embodiment, a mechanism is described to allow a user to control movement of the back support independently of back frame rotation. Said reclining seat can be incorporated into a wheelchair.
A backrest assembly for a wheelchair is known from US 2012/0080919 (EP 2 621 445 A1) which includes a support plate pivotally connected to a seat, wherein the support plate is configured to be pivotally adjusted between upright and reclined positions with respect to the seat; a slide plate slidably secured on a front surface of the support plate; and a backrest adjustment assembly operatively connected to the support plate and the slide plate. The backrest adjustment assembly includes a link configured to adjust the support plate. The slide plate slides over the support plate through the link.
In general a backrest assembly of a wheelchair has a pivot point of a rotational movement of a backrest frame relative to a seat frame during adjustment of the backrest assembly between an upright position and a reclined position. In case said pivot point is not concentric with the hip rotation point of a user of the wheelchair, shear forces will be caused during said adjustment between the backrest assembly, in particular a cushion of the backrest assembly, and the back of the user. In order to compensate said shear forces backrest assemblies have been developed with a support plate pivotally connected to a seat and a slide plate slidably secured on a front surface of the support plate, as described in US 2012/0080919 (EP 2 621 445 A1). In the prior art the link between the slide plate and the support plate is configured to adjust the slide plate with respect to the support plate by connecting a post to a drive bar on a rear surface of the support plate, with the drive bar operatively connecting to a pivot arm on the front surface of the support plate, and the pivot arm operatively connecting to the slide plate via a knob sliding through a slot within the slide plate such that movement of the pivot arm causes the slide plate to slide over the support plate. A recline angle between the backrest and the seat of the known wheelchair thus is determining the rotation of the pivot arm which in turn causes the sliding of the sliding plate via the knob. The effect of the recline angle of the known backrest assembly on the movement of the slide plate is not adjustable.
Thus it would be desirable to provide a backrest assembly for a wheelchair with a reclining seat overcoming the disadvantages known in the state of the art, especially allowing an adjustable compensation of shear forces.